The present invention relates to an improvement in the rotary devices disclosed in U.S. Pat. Nos. 3,101,700 and 3,176,908 dated Aug. 27, 1963, and Apr. 6, 1965, respectively, and each entitled "Rotary Compressor or Engine". For this reason the foregoing patents are incorporated by reference herein. As is well known in the art and as described in said patents, the device is operable either as a compressor or a motor, depending upon the direction of rotation and direction of flow of compressed gas. Thus, while the detailed description will be with reference to a compressor for brevity, it will be understood that a reversal of operation will result in a motor and the invention is not to be limited to either form of operation.
In each of the patented devices there is a recessed rotor and a male rotor, and the two rotors are mounted in a chamber of a housing to rotate in end-to-end relationship with one another about axes of rotation that intersect one another at an acute angle. Also, the rotors are cooperatively engaged with one another and with the wall of the chamber to define an annular operating well or subchamber which is bounded at its periphery by a portion of the wall. In addition, these prior patents the recesses on the recessed rotor are closed ended at the periphery thereof by a portion of the wall of the chamber, and the recesses and blades of the rotors are cooperatively engaged with one another at angular intervals about the opposing end faces of the rotors to subdivide the subchamber into a series of radially oriented cells which coincide with the intervals between pairs of blades and recesses. The end faces are adapted and interrelated with one another, moreover, so that when the rotors are conjointly rotated, the faces alternately converge and diverge between opposite angular stations at which they diverge to a maximum and converge to coincidence with one another, respectively. This has the effect of subjecting the cells to cyclical intake and compression stages on opposite sides of the subchamber, and there is a pair of ports in the housing, one of which opens into the intake side of the subchamber to supply fluid to the cells, and the other of which opens outwardly from the compression side of the subchamber to exhaust the fluid from the cells.
Each of the patented devices suffers from the fact that while it is desirable to locate at least the exhaust port in proximity to the angular station at which the faces of the rotors converge to coincidence with one another, in order to idealize the compression ratio of the device, this location has the disadvantage that it does not offer much room for the port; and where it is not possible or desirable to use the adjacent end wall of the chamber as an additional or alternative location for the port, then the effective area of the port is often so limited as to severely curtail the operating pressure, compression ratio and/or speed of the device.
One object of the present invention is to remove the limitations which are imposed on the patented devices in this regard. That is, the object of this improvement is to increase the available port area, particularly on the exhaust portion of the cycle. The former devices could only provide exhaust from the narrow downstream end of the cells. This improvement provides for exhaust from both ends of the cell simultaneously, thus doubling the available port area. This only becomes possible if the blade and its recess are designed to form a seal on one side and an open passage to its corresponding cell on the opposite side of the blade. Once this is accomplished it is then possible to provide a port to which the compressed air can exit from the contracting cell, through the passage between the blade and recess and into the exhaust port.
In a device of this kind it is essential to provide sealing between the cells formed by the rotors only during the compression part of the cycle and is not necessary during the intake part of the cycle. It is also essential to understand that the thin terminal edge or tip of the blade forms the seal between the cells. As the walls of the cells converge during compression, the sealing line between cells moves from the outer edge or mouth of the recess to the bottom or closed end of the recess as the blade is moved into the recess.
Another object is to provide a means and technique of this nature whereby any compressed fluid remaining in the recesses when the adjacent cells move beyond the exhaust port can expand to release the residual energy contained therein and can thus be put to use rather than lost. Other objects include the provision of a means and technique of this nature whereby the recesses in the grooved rotor can be supplied with fluid in the region of the intake port so as to counteract a tendency for a vacuum condition to occur in the recesses as the blades retract from the same.
Still a further object is to provide a rotary interdigitating blade and recess type compressor having a greatly reduced headspace.
According to the invention, these objects and advantages are realized by providing channels or ports in the aforesaid portion of the wall of the chamber, which are operatively opposed to cells and to the corresponding end openings of the respective recesses in the periphery of the grooved rotor on one side of the subchamber. The recesses which communicate with the port on that side of the subchamber also communicate through passages between the blades and groove sidewall to supply or exhaust fluid to or from the cells as they are supplied with or exhausted of the fluid, depending on the rotational position within the subchamber on which the recess and port are located.
The channel may communicate with the port through a manifold on the housing interconnected with the port, or the port may communicate with the recess by extending the port in the direction of rotation of the rotors. In either case, the channel or port is preferably angularly elongated about the periphery of the recessed rotor in the direction of rotation, to extend between angular stations which are spaced apart by at least the interval between pairs of blades and recesses. The preferred location of the ports is such that the intake port will terminate at the point where the cells formed between the rotors and separated from each other by the blades contain the maximum amount of air or gas, the starting point of the intake port being where the volume of the cells has been reduced by some predetermined amount and was now increasing. In the drawings the exhaust port starting point is shown in a location that would have provided a fifty percent reduction in the volume or capacity of the aforementioned cells. Preferably the exhaust port will terminate a few degrees short of the line of closest approach between the rotors and the intake port will not start for a few degrees beyond that same line of closest approach. Preferably the intake port is wide open to the blades and the blade recess from the aformentioned starting point to a cut-off point just short of where the contained volume starts to contract.
It can be stated that inasmuch as the blades which separate cell from cell during the compression part of the cycle are sealing on one side of the recess and are open to form a passage to a cell on the opposite side of the blade such that the recess becomes an extension of the cell. As such the pressure in the recess will be the same as the pressure in the cell of which it is an extension. If the seal between cells is always at the top edge of the blade, the exhaust port can be extended or a channel provided to reach the cell extension which is actually the trailing blade recess; and if the channel or extended port does not fall below a line traced by the top edge of the blade, compressed air or gas will exhaust into the port but cannot leak back into the next following cell which will not reach design pressure until it has rotated one more cell length.
The channel or port extension over the recess housing can be described as extending back to the trailing blade recess of a cell (two sequential blades define the extent of a cell) from a point opposite the start of the exhaust port in the blade housing and the width of the channel or a port extension being between a line traced by the closed ends of the blade recesses and a line traced by the terminal sealing edge of the blades. Once a cell has rotated to a position where design pressure has been reached and exhaust has started, there is no further need to maintain a seal between that cell and the cell ahead of it since both are in communication with the exhaust port.
A unique feature of the invention is that the shapes of the respective blades and recesses not only provide a supplemental exhaust passage from between the reducing volume of the opposed end faces of the blade and recess rotors which defines the main compression chamber or cell, but further will reduce headspace between the blade and recess at the maximum compression exhaust station. That is, any gap between the downstream side of a blade and downstream wall of a recess at the point of maximum compression will leave residual incompletely compressed and unexhausted air which serves no useful work. By making the blade and recess unsymmetrical and of conforming volumes this headspace is reduced. Furthermore, the blades and recesses are shaped with constantly widening walls or sides from the respective closed end of a recess and tip of a blade for ease of casting during manufacture.